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LXXXIX. Funzioni per le espressioni regolari (POSIX estesa)Nota:
Il PHP, utilizzando le funzioni PCRE,
supporta anche le espressioni regolari con una sintassi compatibile con Perl.
Queste funzioni supportano riconoscimenti "pigliatutto", asserzioni, criteri condizionali,
e diverse altre caratteristiche che non sono supportate dalla sintassi POSIX estesa.
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Queste funzioni per l'espressioni regolari non sono binary-safe. Le funzioni PCRE lo sono.
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In PHP, le espressioni regolari sono utilizzate per complesse
manipolazioni di stringhe. Le funzioni che supportano le espressioni
regolari sono:
Tutte queste funzioni usano una espressione regolare come loro
primo argomento. Le espressioni regolari utilizzate da PHP sono di tipo
POSIX esteso cos� come definito in POSIX 1003.2. Per una descrizione
completa delle espressione regolari POSIX, vedere la pagina del
manuale di regex inclusa nella directory di regex nella distribuzione
di PHP. Questa � in formato man, pertanto per poterle leggere occorre
eseguire man /usr/local/src/regex/regex.7.
Esempio 1. Esempi di espressione regolare ereg ("abc", $string);
/* Restituisce vero se "abc"
viene trovata ovunque in $string. */
ereg ("^abc", $string);
/* Restituisce vero se "abc"
viene trovata all'inizio di $string. */
ereg ("abc$", $string);
/* Restituisce vero se "abc"
viene trovata alla fine di $string. */
eregi ("(ozilla.[23]|MSIE.3)", $HTTP_USER_AGENT);
/* Restituisce vero se il browser
� Netscape 2, 3 oppure MSIE 3. */
ereg ("([[:alnum:]]+) ([[:alnum:]]+) ([[:alnum:]]+)", $string,$regs);
/* Posizione tre parole separate da spazio
in $regs[1], $regs[2] e $regs[3]. */
$string = ereg_replace ("^", "<br />", $string);
/* Posiziona il tag <br /> all'inizio di $string. */
$string = ereg_replace ("$", "<br />", $string);
/* Posiziona il tag <br /> alla fine di $string. */
$string = ereg_replace ("\n", "", $string);
/* Toglie ogni carattere di invio
da $string. */ |
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- Sommario
- ereg_replace -- Sostituzioni con espressioni regolari
- ereg -- Riconoscimento di espressione regolare
- eregi_replace -- Sostituzioni con espressioni regolari senza distinzione tra maiuscole e minuscole
- eregi -- Riconoscimento di espressioni regolari senza distinzione tra maiuscole e minuscole
- split -- Suddivide una stringa in una matrice utilizzando le espressioni regolari
- spliti --
Suddivide una stringa in una matrice usando le espressioni regolari senza distinguere tra
maiuscole e minuscole
- sql_regcase --
Genera una espressione regolare per riconoscimenti senza distinguere tra maiuscole e minuscole
User Contributed Notes
Funzioni per le espressioni regolari (POSIX estesa) |
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07-Mar-2001 06:38 |
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If you don't have commandline access to the manpage cited above, note that
the "POSIX 1003.2 Regular Expressions" manpage is also widely
re-published on the web. See, for instance:
The
"POSIX 1003.2 Regular Expressions" manpage provides a good basic
reference for the syntax used by ereg_* functions. Most tutorials on
"extended regular expressions" are also applicable.
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[email protected]
07-Mar-2001 01:53 |
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Dario seems to have made a nice tutorial about regular
expressions:
Thanks
Dario! ...
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[email protected]
18-Dec-2001 12:39 |
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I noticed Cyro's link had gone old. So I made copy of the regex manpage and
placed it on my site. You can get it from the following
address:
This
is primarily for Windows users, who have no access to the man pages in
Linux distributions.
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03-Feb-2002 02:02 |
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if you are looking for the abbreviations like tab, carriage return,
regex-class definitions
you should look here:
some
excerpts:
\a control characters bell
\b backspace
\f form
feed
\n line feed
\r carriage return
\t horizontal
tab
\v vertical tab
class example
\cLu all uppercase
letters
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[email protected]
21-Feb-2002 04:12 |
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It's easy to exclude characters but excluding words with a regular
expression is a bit more tricky. For parentheses there is no equivalent to
the ^ for brackets. The only way I've found to exclude a string is to
proceed by inverse logic: accept all the words that do NOT correspond to
the string. So if you want to accept all strings except those _begining_
with "abc", you'd have to accept any string that matches one of
the following:
^(ab[^c])
^(a[^b]c)
^(a[^b][^c])
^([^a]bc)
^([^a]b[^c])
^([^a][^b]c)
^([^a][^b][^c])
which, put together, gives the regex
^(ab[^c]|a[^b]c|a[^b][^c]|[^a]bc|[^a]b[^c]|[^a][^b]c|[^a][^b][^c])
Note
that this won't work to detect the word "abc" anywhere in a
string. You need to have some way of anchoring the inverse word
match
like: ^(a[^b]|[^a]b|[^a][^b]) ;"ab" not at begining
of line
or: (a[^b]|[^a]b|[^a][^b])& ;"ab" not at end
of line
or: 123(a[^b]|[^a]b|[^a][^b]) ;"ab" not after
"123"
I don't know why "(abc){0,0}" is an
invalid synthax. It would've made all this much simpler.
Slightly off-topic, here's a regex date validator (format yyyy-mm-dd,
remove all spaces and linefeeds):
^(19|20)([0-9]{2}-((0[13-9]|1[0-2])-(0[1-9]|[12][0-9]|30)|
(0[13578]|1[02])-31|02-(0[1-9]|1[0-9]|2[0-8]))|([2468]0|
[02468][48]|[13579][26])-02-29)$
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luciano_at_braziliantranslation.net
03-Mar-2002 07:15 |
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mholdgate wrote a very nice quick reference guide in the next page (),
but I felt it could be improved a
little:
________________
^ Start of line
$ End of
line
n? Zero or only one single occurrence of character
'n'
n* Zero or more occurrences of character 'n'
n+ At least one
or more occurrences of character 'n'
n{2} Exactly two occurrences of
'n'
n{2,} At least 2 or more occurrences of 'n'
n{2,4} From 2 to 4
occurrences of 'n'
. Any single character
() Parenthesis to group
expressions
(.*) Zero or more occurrences of any single character, ie,
anything!
(n|a) Either 'n' or 'a'
[1-6] Any single digit in the
range between 1 and 6
[c-h] Any single lower case letter in the range
between c and h
[D-M] Any single upper case letter in the range
between D and M
[^a-z] Any single character EXCEPT any lower case
letter between a and z.
Pitfall: the ^ symbol only acts as an
EXCEPT rule if it is the
very first character inside a range, and it
denies the
entire range including the ^ symbol itself if it appears
again
later in the range. Also remember that if it is the first
character in the entire expression, it means "start of
line".
In any other place, it is always treated as a regular ^
symbol.
In other words, you cannot deny a word with ^undesired_word
or a group with ^(undesired_phrase).
Read more detailed regex
documentation to find out what is
necessary to achieve
this.
[_4^a-zA-Z] Any single character which can be the underscore
or the
number 4 or the ^ symbol or any letter, lower or upper
case
?, +, * and the {} count parameters can be appended not only
to a single character, but also to a group() or a
range[].
therefore,
^.{2}[a-z]{1,2}_?[0-9]*([1-6]|[a-f])[^1-9]{2}a+$
would
mean:
^.{2} = A line beginning with any two characters,
[a-z]{1,2} = followed by either 1 or 2 lower case letters,
_? =
followed by an optional underscore,
[0-9]* = followed by zero or
more digits,
([1-6]|[a-f]) = followed by either a digit between 1 and
6 OR a
lower case letter between a and f,
[^1-9]{2} = followed
by any two characters except digits
between 1 and 9 (0 is possible),
a+$ = followed by at least one or more
occurrences of 'a' at
the end of a line.
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[email protected]
07-Mar-2002 05:26 |
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sorry to be picky here but saying ^ is beginning of a line or $ is end of
line is rather misleading, if you're working on a daily basis with
regexes.
it might be that it is most of the time correct BUT in
some occasions you'd be better off to think of ^ as "start of
string" and $ as "end of string".
there are ways to
make your regex engine forget about your system's notion of a newline,
it's what is commonly refered to as multiline regexes...
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[email protected]
08-Mar-2002 05:33 |
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Follow-up to my previous post:
Some simple optimization allowed me to
realize that excluding a word at the beginning of a string has a degree of
complexity O(n) rather than O(n^2). I only had to follow the
logic:
if str[0] != badword[0] then OK
else
if str[1] !=
badword[1] then OK
else
if str[2] != badword[2] then OK
else ...
So excluding the word 'abc' at the beginning of a string
is much more simple than I had made it out to be:
^([^a]|a[^b]|ab[^c])
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[email protected]
09-Mar-2002 05:40 |
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Sadly, the Posix regexp evaluator (PHP 4.1.2) does not seem to support
multi-character coallating sequences, even though such sequences are
included in the man-page documentation.
Specifically, the man-page
discusses the expression "[[.ch.]]*c" which matches the first
five characters of "chchcc". Running this expression in
ereg_replace generates the error "Warning: REG_ECOLLATE".
(Running an equivalent expression with only one character between the
periods does work, however.)
Multi-character coallating sequences
are not supported!
This is really, really too bad, because it would
have provided a simple way to exlude words from the target.
I'm
going to go learn PCRE, now. :-(
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[email protected]
22-Aug-2002 02:40 |
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Something that really got me: I'm used to using Perl's regexps, and so I
used \s to check for a whitespace character in a password on a website. My
PHP book (Wrox Press, Professional PHP Programming) agreed with me that
this is exactly the same as [ \r\n\t\f\v], but it's NOT. In fact, what it
did was keep anyone from joining the site if they put an 's' in their
password! So beware, check for subtle differences between what you're used
to and PHP.
[[:space:]] works fine, by the way.
I'm going to
use the pcre functions from now on... I like Perl :o)
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